The structure-function relationships of biological materials are critical to understating tissue development, function, disease, and therapy. We use custom-built devices to simultaneously study structure and mechanics of biological tissues.
Fluorescence movie of human knee cartilage under shear. The cartilage is stained green, then photobleached, to allow for calculation of strains and displacements, and in turn for calculations of local moduli. Notice that the upper region, close to the articular surface, is much more compliant than the bulk.
Time lapse video of the front view of a Medicago root growing on an inclined plane within a gel. One photo is taken an hour over a course of 2 weeks. Note the root waving as it hits the glass plane.
Articular cartilage, the soft connective tissue that coats bones in joints, is a highly complex and inhomogeneous material. It is made up of a fluid-saturated, cross-linked network of collagen fibrils whose orientation and porosity vary with depth from the articular surface. Interspersed among the network are cells and highly charged molecules called proteoglycans. Cell shape, cell density and proteoglycan density are all also spatially dependent.
Local mechanical properties in articular cartilage and other biological tissues are typically measured by tracking the displacement of cells, cell nuclei and other fiducial markers using particle image velocimetry (PIV) and other feature-tracking methods (see "Quasi-Static Shear Mechanical Properties of Articular Cartilage"). However, these techniques are limited in spatial resolution by the density of trackable markers. In adult articular cartilage, intervertebral disk and other soft tissues, cells can be very sparse. Therefore, we have developed grid-resolution automated tissue elastog
Our current work is focused on characterizing healthy breast tissue. Stay tuned for more results...
As global climates change, agriculture and crop breeding programs must increase productivity to meet the demands of growing populations while simultaneously facing decreases in soil quality.
Articular cartilage (AC), a biological tissue that protects and lubricates joints, plays a critical role during healthy locomotion. While much is known about this tissue's biochemistry and compressive mechanical properties, comparatively less attention has been given to its shear mechanical properties. This represents a critical knowledge gap because cartilage tissue experiences significant shear under normal loading conditions, and may indeed most frequently fail in such circumstances.
Articular cartilage (AC), a biological tissue that protects and lubricates joints, plays a critical role during healthy locomotion. Ongoing work in the Cohen lab has been examining the spatially heterogeneous mechanical properties of this tissue using confocal rheology. This technique allows us to simultaneously deform the tissue with a known stress and measure the local strain field. From this information, we can calculate the local shear properties.
